The invention is related to a housing for a pneumatic power booster of a type comprised of a first and a second bowl shaped housing half which are coated with a protective surface finish. The housing halves are assembled with their open sides facing each other and telescoped one into the other and permanently fixed to each other. The first housing half has a rim which is bent out and back reversely and the second housing half is formed with an edge of a preferably cylindrical configuration. An elastic diaphragm is compressed between the housing halves to create a seal. The diaphragm comprises a movable wall dividing the inner space of the housing into two pneumatic chambers. The edge of the second housing half is formed with a plurality of uniformly distributed circumferential slots having portions which are parallel to the cylindrical edge and to the bent-over rim of the first housing half, so that localized zones weakened in the radial direction are formed.
This invention is also concerned with a process for manufacture of this type of housing.
A housing of this kind and a process for its manufacture are described in European patent application EP-A-0 300 857. The housing half having the cylindrical edge is formed about its edge with a plurality of circumferential slots which are symmetrically distributed about its circumference and preferably have an oval or rectangular shape, and which, with the outer edge of the cylindrical edge, define web-like zones weakened in the radial direction, which upon the two housing halves being telescoped one into the other are pressed in in such a way that their center portions move away in an axial direction from a plane running parallel to the bent-over rim of the other housing half through the end points of the webs. In this manner, the risk of corrosion is largely eliminated in particular along the connecting seam of the two housing halves.
In the prior-art pneumatic power booster, the extremely high surface tension which occurs due to the pressing-in of the webs in particular in their central portions, on the inside and on the outside, may lead to damaging of the applied protective coating layer. Those portions which are no longer protected against corrosive attack, are subjected to a considerable axial stress especially during operation of the power booster, and thus are particularly subject to corrosive attack and can, upon an extended service period, cause the failure of the power booster.
It is, therefore, the object of the present invention to provide a coupling of the two housing halves of a pneumatic power booster which does not result in areas of high surface tension.